The present application claims the right of foreign priority of German Application No. DE 299 23 063.5 filed Dec. 31, 1999, the subject matter of which is incorporated herein by reference.
The invention relates to a device for indicating the calcification status of flow heaters, particularly in espresso machines, with the flow heater having a cold-water inlet and a hot-water outflow.
In the operation of a flow heater of this type, a pump conveys water from a cold-water reservoir through the cold-water inlet and adjoining, indirectly-heated pipes of the flow heater, where the water is heated. Afterward, the hot or scalding water exits a hot-water outflow of the flow heater and is pumped into a brewing apparatus. The water is heated to about 96xc2x0 C. in the flow heater, also referred to as a thermoblock. Particularly if the cold water is very hard, sediment builds up in the heated pipesxe2x80x94also called flow-through pipesxe2x80x94after an operational time that is a function of the degree of hardness. The sediment increasingly narrows the clearance cross section of the flow-through pipes, thereby decreasing their efficiency and limiting the function of the flow heater, until the heater becomes blocked. The functioning capability of the flow heater can be restored through the use of commercially-available decalcifying agents, but this is an additional procedure that is often avoided because it is relatively laborious. Therefore, indicators are provided for clearly indicating when decalcifying is necessary.
Counters that indicate the number of batches through the flow heater are known as indicator devices. Because the throughput quantities for preparing a beverage lie within a predetermined range, the local degree of water hardness can be used to find an empirical value that determines how many batches should be processed between decalcifying procedures. This device, however, yields only imprecise results and approximations of the actual calcification status.
A measurement system known from the state of the technology uses the external temperature of the flow heater to estimate its calcification status. As the thermally-insulating calcification layer builds up, the external temperature increases due to the less effective dissipation of generated heat by the water flowing through the flow-through pipes. This thermal measuring device, however, operates imprecisely, because the measurable external temperature of the flow heater is dependent on further parameters, particularly previous brewing processes, if the required external heating of the flow heater has not diminished completely before the start of a new brewing process with a detection of the external temperature.
It is also known to insert a flow detector into the supply line or discharge line of the flow heater for measuring the change in the flow speed, namely a decrease in the speed with increased calcification in the flow heater. A flow detector of this type is, however, technically too complicated for applications such as small espresso machines intended for household use.
It is therefore the object of the present invention to provide a device for indicating the calcification status of flow heaters that is technically uncomplicated, yet permits a fairly precise indication of the actual calcification status of the flow heater. This indication is intended to be a direct measure for the present calcification status, without a separate, subsequent accounting of further parameters such as the degree of hardness of the cold water.
The above object is achieved according to the present invention by a device for indicating the calcification status of a flow heater having a cold-water inlet line and a hot-water outflow line, with the device comprising a differential-pressure fluid gauge having first and second pressure chambers and a diaphragm disposed between and separating the fist pressure chamber from the second pressure chamber. The first pressure chamber is in a fluid-conducting connection with the cold-water inlet line, the second pressure chamber is in a fluid-conducting connection with the hot-water outflow line, and, the diaphragm acted upon by the pressure difference between the first pressure chamber and the second pressure chamber is coupled to an indicator.
The solution is based on the principle that the flow through the flow heater is detected by an uncomplicated differential-pressure fluid gauge chamber, in which a diaphragm separates two pressure chambers that act in opposite directions on the diaphragm. Of the pressure chambers, the first is in a fluid-conducting connection with the cold-water inlet of the flow heater, and the second is connected to the hot-water outflow of the heater. The outward bending of the diaphragm that results due to the pressure difference between the cold-water inlet and the hot-water outflow, and thus in the two chambers, during the operation of the flow heater stands as a measure for the flow resistance in the flow heater, and therefore the calcification of the heater. The deformation of the resiliently-yielding diaphragm itself can indicate the calcification of the flow heater, for example if a portion of the diaphragm projects out of the housing of the differential-pressure fluid gauge chamber. The diaphragm is, however, preferably connected to further mechanical indicator elements, such as a pointer that moves relative to fixed markings, or electrical indicator elements, such as a light-emitting-diode (LED) display that is actuated by the diaphragm for signaling the need to decalcify the machine. This represents a reliable decalcification indicator. It must be borne in mind here that, according to the invention, the differential pressure with a water hardness of about 20xc2x0 increases by about 1 bar after approximately 40 liters have passed through the flow heater, which can effect a considerable change in the status of the indicator elements.
According to a preferred embodiment, the diaphragm is advantageously embodied as a catch-spring disk that is dimensioned to snap when a predetermined differential pressure equal to a maximum permissible differential pressure is attained. This snapping is therefore effected at a differential pressure that is predetermined by the dimensioning of the catch-spring disk, and takes into consideration a differential-pressure tolerance range with which possible pressure influences due to a throttle effectxe2x80x94which varies within limitsxe2x80x94of a brewing head connected to the hot-water outflow can be taken into consideration.
To avoid residual water in the differential-pressure fluid gauge chamber, according to a feature of the invention, the chamber is disposed above the flow heater, with the diaphragm being oriented nearly vertically. With this positioning, residual water can flow out of the chambers of the differential-pressure fluid gauge chamber due to the effect of gravity. The residual water is also sucked out after the brewing process due to a corresponding vacuum in the flow heater and the brewing head.
As an alternative to the above-mentioned indicators, optical indicator elements can be connected to the diaphragm. The elements can include a counter in particular.
Alternatively, electrical indicator elements that can be controlled by the diaphragm can be provided in place of the optical indicator elements. These indicator elements can comprise an LED in a circuit with a switch contact that is actuated by the diaphragm.